A dust collector can experience moisture problems even if moisture is only occasionally present. The moisture may appear only during certain times of the day, during certain seasons of the year, or as a result of special occurrences affecting the process airstream. If the dust collector is located outdoors and exposed to daily and seasonal weather changes, moisture may condense on the collector's inside surfaces when the air temperature drops below the dew point inside the collector.
The dew point is the temperature at which an air-vapor mixture becomes saturated and incapable of holding more water vapor. The dew point temperature varies depending on the amount of moisture in the air at any given time, and hot air can hold more water vapor than cooler air. As the air temperature falls below the dew point, water vapor begins to condense out of the air and form liquid water droplets. Examples of this phenomenon include fog forming in very humid air, dew forming on grass, and frost forming on a car windshield.
To determine whether moisture is intermittently present in your dust collector, check inside the dirty air chamber when the possibility of moisture is high and the dust collector isn’t operating. Inspect the inside walls of the dust chamber for drops of moisture, wet dust clumps, or areas of rust formation. While wearing appropriate protective clothing, carefully remove some dust and place it onto a paper towel. Squeeze the paper towel with the dust sample inside and see if any moisture or oils transfer to the paper towel. If any noticeable amount of moisture transfers, a moisture problem is present and should be corrected. Don’t perform this test if your dust is toxic, however. Toxic dust should only be handled by professionals trained in handling such materials. And remember, while the moisture may be intermittent and can disappear before anyone notices, the damage may be permanent, especially to cellulose cartridge filters.
Causes of moisture in dust collectors
Key factors that can cause moisture to be present in a dust collector include:
Hygroscopic dust. The dust being collected may be hygroscopic and contain moisture. Sawdust, for example, typically has a moisture content of 19 percent.
Mists or sprays. Mists or aerosol sprays may be intermittently or continuously added to the process airstream. For example, machine cutting tools often require coolant sprays to prevent overheating during operation. A hood collecting dust generated by the cutting tool may also draw moisture from the coolant spray into the dust collection airstream.
Ambient humidity. Humidity changes caused by wind direction or other weather conditions can increase the moisture content of the process airstream.
Process airstream cooling. The air temperature at the system’s dust collection points may be considerably hotter than in the dust collector, particularly if the dust collection point is located over a heat source, the dust collector is located outside the building in an area with cold weather conditions, or the process airstream travels a long distance between the dust collection point and the dust collector.
Compressed-air moisture. The compressed air for the pulse-jet cleaning system may contain excessive moisture. A pulse-jet cleaning system directs intermittent high-speed pulses of compressed air at the clean side of the dust collector filters to dislodge caked dust and prolong filter life. If the compressed air contains excessive moisture, the filter media can become soaked, preventing caked dust from dislodging from the filter during the cleaning cycle and causing problems for both bag and cartridge filters.